I apologize if this is an obvious question, but I have not been able to find the answer in a dictionary.
The specific problem I'm having is distinguishing between
[certificate] which certifies the suitability of a product for [purpose] vs. [certificate] which certifies the fitness of a product for [purpose].
Personally I feel suitability has a slightly more positive bias, but at the same time might be less rigorous, while fitness seems more rigorous but also more neutral.
If anyone can explain the exact difference between these two I would be much obliged.
Best Answer
Here are the definitions, not for products but for human competence, according to the DOD.
If I understand well, and adapted for a product, suitability, would be, for example, that a knife is suitable to cut a steak (whatever the state of its blade) but could not be called fit to cut the steak if it's not sharp enough to do the job.
See also this reference about commercial transactions and fitness vs suitability in the Australian legal system: sydney.edu.au/law/slr/slr_32/slr32_2/Pearson.pdf.
It's might be confusing though. The author seems to say that suitabilty is the continuation, a more modern verson of fitness but in the body of the text he sometimes uses the term as synonyms...